Brake

A brake is a device for slowing or stopping the motion of a machine or vehicle, or alternatively a device to restrain it from starting to move again. The kinetic energy lost by the moving part is usually translated to heat by friction. Alternatively, in regenerative braking, much of the energy is recovered and stored in a flywheel, capacitor or turned into alternating current by an alternator, then rectified and stored in a battery for later use.

Note that kinetic energy increases with the square of the velocity ("E" = 1/2·"m"·"v"² relationship). This means that if the speed of a vehicle doubles, it has four times as much energy. The brakes must therefore dissipate four times as much energy to stop it and consequently the braking distance is four times as long.

Brakes of some description are fitted to most wheeled vehicles, including automobiles of all kinds, trucks, trains, motorcycles, and bicycles. Baggage carts and shopping carts may have them for use on a moving ramp.

Some aeroplanes are fitted with wheel brakes on the undercarriage. Some aircraft also feature air brakes designed to slow them down in flight. Notable examples include gliders and some WWII-era fighter aircraft. These allow the aircraft to maintain a safe speed in a steep descent. The Saab B 17 dive bomber used the deployed undercarriage as an air brake.

Deceleration and avoiding acceleration when going downhill can also be achieved by using a low gear; see engine braking.

Friction brakes on cars store the heat in the rotating part (drum brake or disc brake) during the brake application and release it to the air gradually.

Effects on noise pollution

The action of braking for motor vehicles produces recognizable sound level emissions, varying with the specific tire types and with the roadway surface type produces considerable effect upon sound levels or noise pollution emanating from moving vehicles. [ [http://www.springerlink.com/content/x1707075n815g604/ C.Michael Hogan, " Analysis of highway noise", Journal of Water, Air, & Soil Pollution, Volume 2, Number 3, Biomedical and Life Sciences and Earth and Environmental Science Issue, Pages 387-392, September, 1973, Springer Verlag, Netherlands ISSN 0049-6979] ] There is a considerable range in acoustical intensities produced depending upon the specific tire tread design and the rapidity of deceleration required to slow the vehicle.

Hypermiling

Because braking (absent regenerative braking) converts kinetic energy into heat energy, it wastes energy that was used earlier to gather speed. Additionally, regenerative braking is not 100% efficient at recovering energy. Some drivers use various techniques to minimize braking to save fuel (see hypermiling).

ee also

* Archaic past tense of break (see )
* Air brake (aircraft)
* Air brake (rail)
* Air brake (road vehicle)
* Bicycle brake systems
* Brake-by-wire (or electromechanical braking)
* Line lock
* Brake lining
* Brake pad
* Brake shoe
* Bundy tube
* Disc brake
* Drum brake
* Electromagnetic brake
* Electronic Parking Brake
* Engine braking
* Hand brake
* Hydraulic brake
* Jake brake also known as J braking
* Overrun brake
* Parking brake
* Railway brake
* Regenerative braking
* Threshold braking
* Trail braking
* Vehicle brake

References

External links

* [http://www.carbibles.com/brake_bible.html The Brake Bible]
* [http://auto.howstuffworks.com/brake.htm How Stuff Works - Brakes]
* [http://www.autocarrepair.net/Brake-System-Repairs.html High Quality Brake System Repairs Guide]
* [http://ebc-brakes.activebrakesdirect.com/ Brakes News Blog]
* [http://www.black-ridge.com/brakes-general.htm How to know when to replace your brakes]
* [http://www.opencortex.org/cn00000233 Resource on Stanfords solar car brakes]